The present invention relates to a nuclear reactor and, more particularly, to a novel construction of nuclear reactor which can provide greater flow rate of coolant flowing through the reactor core. The construction of a nuclear reactor in accordance with the invention is suitable for use particularly in small-sized nuclear reactors.
Most nuclear reactors commercially operating presently are light-water nuclear reactors of large capacities having electric power output of an order of 400 MWE. A boiling water reactor, which is known as a kind of light-water reactor, has a pressure vessel and a reactor core disposed in the pressure vessel. The reactor core includes a multiplicity of fuel assemblies. Control rods for controlling the power of the reactor are adapted to be inserted into the reactor core from the lower side of the reactor core. The boiling water reactor has also a recycling system for recycling a coolant through the reactor core and serving also as means for effecting a fine adjustment of the power of the nuclear reactor. The steam generated in the pressure vessel of the nuclear reactor is introduced into a steam turbine to drive the latter and is then condensed in a condenser. The condensate is then recycled as the coolant into the pressure vessel.
Another typical example of a light-water reactor is a pressurized water reactor which is constituted by a pressure vessel containing a reactor core having a multiplicity of fuel assemblies, a steam generator and a primary cooling system which forms a closed loop including the pressure vessel and the steam generator. The hot coolant after being heated in the reactor core is introduced into the steam generator through the pipe of the primary cooling system to make a heat exchange with feed water fed into the steam generator. The coolant, the temperature of which has been lowered as a result of the heat exchange, is returned from the steam generator into the pressure vessel through the pipe of the primary system. On the other hand, the feed water is evaporated to become steam as a result of the heat exchange. The steam is introduced into a turbine to drive the latter and, thereafter, condensed in a condenser. The condensate is returned as the feed water to the steam generator.
The capacity of the light-water nuclear reactors is getting larger year by year. On the other hand, however, there is an increasing demand for nuclear reactors of smaller capacities having electric power output of less than 200 MeW, as the power source of small-scale power generating equipment and the heat source for a district heating system.